We propose to perform a pre/post longitudinal study of Medicaid managed care and its impact on primary care physicians practicing in the major urban counties of California. The overall objective of our study is to evaluate how the "Medicaid managed care revolution" is affecting primary care physicians and the populations they serve. We are particularly interested in determining whether market changes are differentially affecting physicians depending on their demographics, qualifications, type of practice, and patient characteristics. In 1996, prior to a widespread implementation of Medicaid managed care, we conducted a mailed survey of a probability sample of primary care physicians providing care in the thirteen largest urban counties of California. Physicians from under-represented minority groups were over- sampled. Subjects were questioned about such issues as their demographics and training, the characteristics of the patients in their practice, policies on accepting or limiting new Medicaid patients, contractual arrangements with IPAs and HMOs (including exclusion from networks), attitudes and cultural competence in caring for Medicaid and minority patients, and attitudes toward shifting Medicaid to a managed care format. We are proposing to perform a follow-up wave of surveys to be administered in 1998, approximately 18 months after the baseline survey . The sample of physicians in the follow-up survey wave will include all 947 responders from the baseline wave of surveys. The follow up survey will consist of similar questions as were used in the baseline study so that we can analyze practice changes over time. The timing of the follow up survey, 18 months after the baseline survey is based on our expectation that many of the counties from which we drew our physician sample will have shifted large proportions of their Medicaid populations to Medicaid managed care in the interim. At baseline, 3 counties were functioning under mandatory Medicaid managed care. Since the performance of the baseline survey, 5 more counties have implemented mandatory Medicaid managed care, and it is likely that others will as well before the performance of the follow up survey. This change for some but not all of our physician subjects provides an excellent "natural experiment" opportunity to examine the impact of mandatory Medicaid managed care isolated from secular changes in the health care marketplace.